I know this is already a solved issue. But, on Windows XP and ZDesktop Beta1, I had to make some minor change to get it to work, so posting this just in case.
CD to..
C:\Documents and Settings\<USERNAME>\Local Settings\Application Data\Zimbra\zdesktop
java -cp jetty\lib\log4j-1.2.8.jar;jetty\common\lib\commons-httpclient-3.0.jar;jetty\common\lib\mail.jar;jetty\common\lib \commons-logging.jar;jetty\common\lib\commons-codec-1.3.jar;jetty\common\lib\json.jar;jetty\common\lib \dom4j-1.5.jar;jetty\common\lib\zimbracommon.jar;jetty\we bapps\service\WEB-INF\lib\zimbrastore.jar -Dzimbra.config=conf\localconfig.xml com.zimbra.cs.zimlet.ZimletUtil deploy zimlets\<ZIMLET.zip> |